The overall objective of the proposed research is to characterize the determinants of respiratory muscle function in diseases which predispose to respiratory failure. The projects described for the coming year focus on the effect of undernutrition on respiratory muscle strength and endurance in patients with chronic obstructive pulmonary disease (COPD), the relationship between respiratory muscle contractile effort, fatigue, and the timing of contraction to exercise-induced dyspnea in COPD, the effects of inspiratory muscle training on exercise capacity, and assessment of the balance between respiratory muscle capacity to perform work on the respiratory system and the work which must be pefromed to sustain given levels of ventilation. The techniques to be employed in these investigations include anthropometric assessment of body composition, indirect and direct assessment of respiratory muscle mass, measurement of respiratory muscle strength during maximum static efforts from mouth, pleural and gastric pressures, measurement of respiratory muscle length or length changes using roentgen techniques and direct measurement, and respiratory muscle electromyography using surface and esophageal electrodes. The electromyographic signals will be processed in time or frequency domains to quantify the presence or absence of muscle activity, the intensity of the activity, and whether or not fatigue is impending. Respiratory system mechanics and pressure-time integrals will be assessed using a pulsed-flow technique.